The present invention relates to a to a method for operating a hydraulic system of an automatic transmission of a motor vehicle.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
In a dual clutch transmission two sub-transmissions enable a fully automatic gear change without interruption of traction. A torque is transmitted via one of two clutches, which connects the two sub-transmissions with the drive. The clutches and the actuators for engaging the gears are hydraulically controllable via a hydraulic system.
In the hydraulic system known from the state-of-the-art the low-pressure circuit has a cooling pump and the high-pressure circuit has a charge pump with which the pressure accumulator is charged to the required accumulator pressure. The two hydraulic pumps are driven by a common electric motor via a common drive shaft. The electric motor is controlled via a control device. When a requirement to charge the pressure accumulator exists, the electric motor is operated with a charge rotational speed. As an alternative and/or in addition the electric motor is operated with a cooling rotational speed for example when a requirement for cooling exists (i.e., when charging is not required). In addition the high-pressure circuit and low-pressure circuit can be connected via a bypass line with integrated control valve. The control valve can be switched in dependence on the accumulator pressure in the high-pressure circuit without requiring further external energy, i.e., automatically, between a charging position and a non-charging position (i.e., cooling position). In the charging position the hydraulic system operates in the charging mode (i.e., the charge pump is fluidly connected with the high-pressure circuit) at high pump load with correspondingly great actual power consumption. On the other hand in the non-charging position (i.e., cooling position) of the control valve the hydraulic system operates for example in a cooling operation or in another operation, for example a filter cleaning operation.
For reasons of clarity in the following the term cooling position of the control valve is used in most cases. It is noted that the cooling position and the non-charging position of the control valve are identical. In addition for reasons of clarity the terms cooling operation and cooling rotational speed are used in the following. The cooling operation is only an example for a non-charging operation and hence term cooling operation can be replaced with the more general term non-charging operation.
In the cooling position of the control valve the charge pump, beside the cooling pump, is also fluidly connected with the low-pressure circuit and decoupled from the high-pressure circuit. In the cooling operation the hydraulic pumps operate—in contrast to the charging operation—at a lower pump load with correspondingly lower actual power consumption.
In the state-of-the-art the control device can operate in a provisioning mode, in which an intent of the user to start operation of the vehicle is detected via appropriate sensors and/or determined based the occurrence of predefined events. When this is the case it is further tested whether a requirement for charging the pressure accumulator exists. When this criterion is also satisfied a full charge operation is initiated in which the pressure accumulator is filled up to a maximal accumulator pressure. This ensures that the automatic transmission is ready for operation when subsequently initiating operation of the vehicle. The pressure accumulator is therefore always fully charged even when subsequently operation of the vehicle is not initiated but the vehicle is only loaded.
It would therefore be desirable and advantageous to provide a method for operating a hydraulic system of an automatic transmission, in which unnecessary charging processes up to the complete filling of the pressure accumulator are avoided, the number of charging cycles of the vehicle battery is reduced and generally energy can be saved.